Journal of advanced materials and processing
Volume:9 Issue: 2, Spring 2021

Cerium oxide (ceria, CeO2) is a biocompatible ceramic oxide with a wide range of applications as catalysts, fuel cell systems, and sensors. In the present study, CeO2 NPs were added to a zinc phosphate bath as an accelerator. The microstructural, morphological, and phase studies of coatings formed in the phosphating bath with and without CeO2 NPs, were performed by scanning electron microscopy (SEM), field emission-SEM (FE-SEM), and X-ray diffraction spectroscopy (EDS). Besides, the corrosion behavior of phosphate coatings containing 0, 0.04, 0.07, and 0.1 g/L of CeO2 NPs was evaluated using the Tafel polarization method and electrochemical impedance spectroscopy (EIS). The results showed significant differences in the microstructure, roughness, and phase structure of phosphate coatings with and without CeO2 NPs. The optimum addition of CeO2 NPs to the phosphating bath was equal to 0.07 g/L, in which, as compared to typical phosphate coating, the coating weight increased from 0.51 to 1.73 mg/cm2 while the corrosion current density decreased from 12.5 to 2.2 µA/cm2. Furthermore, the coating porosity decreased from 13.9 to 1.7 percent due to creating a denser coating with much better coverage by CeO2 NPs.

In this study, the effect of applying electromagnetic vibration simultaneously along with welding to improve the mechanical properties of the Incoloy 825 superalloy weld metal was investigated. The samples were welded by the GTAW method and the simultaneous application of electromagnetic vibration under voltages from zero to 30 volts. The impact toughness and hardness of the weld metals produced by different voltages were measured. The microstructure of base and weld metals was investigated by an optical microscope and SEM. Microstructural studies showed that the weld metal has a fully austenitic matrix with fine precipitates on the grain boundaries and within the grains. It was found that the application of electromagnetic vibration by the fragmentation of the dendrite tips and their entry to the weld metal molten pool contribute to the increasing of heterogeneous nucleation and therefore grain refinement. The result of impact and hardness tests depicted that by applying the electromagnetic vibration the impact toughness and hardness of the weld metal are increased from 27.7 to 35.3 jols and from 205.5 to 257.7 Vickers, respectively. It was found that electromagnetic vibration improves the hardness and impact energy of the weld metal by affecting the parameters, refined equiaxed dendrites, structure within grains and better distribution of precipitates.

Carbon bonded alumina foam filters have been successfully using for steel melt filtration. Enhancement of the filtration capacity of Al2O3-C foam filters is a key factor in order to make them applicable to be used for large steel casting parts or continuous casting of steel. In the present study, filtration performance of hercynite coated carbon bonded alumina foam filters containing 1 Wt.% of nano-TiO2 were evaluated by the exposure to an Al-killed 304 low carbon stainless steel melt. Successful impingement of steel melt into the filters revealed the filter structure strength and effectiveness under casting temperature and molten metal exposure conditions. Microstructural investigations using a field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) analysis of the active hercynite coated filter surfaces after steel melt filtration revealed the entrapment of the oxide inclusions from the steel melt on the surface of the filter. In addition, filtration mechanisms for whiskers and dendritic Al2O3, and hercynite inclusions at different Al/oxygen activity conditions of the steel melt were proposed. To this end, the feasible potential for the application of hercynite coated Al2O3-C filters for low and ultra-low carbon steel casting processes could be promising.

In this paper, the optimal parameters of the FSW welding process to improve the joint's mechanical properties are obtained using robust multi-objective optimization. First, the properties of the weld zone, such as the chemical composition of the weld, are investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The hardness and tensile properties of the weld were investigated to evaluate the mechanical properties of the joint. The results show at the AA7075 side, the highest hardness is observed in the TMAZ, and the hardness is reduced in the SZ. Tensile testing revealed that the joint's mechanical characteristics were superior to those of the basic metals. In order to obtain the relationship between the process input parameters and the mechanical properties of the obtained joint, an artificial neural network model (ANN) was used. The relationship obtained by ANN was then used to obtain the optimal values of process parameters considering uncertainties in a robust optimization algorithm. In this way, using such an obtained feed-forward neural network and the Monte Carlo simulation, a multi-objective genetic algorithm is used for the robust Pareto optimization of the friction stir welding parameters having probabilistic uncertainties in parameters. Finally, the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) was used to get the best optimum solution. The robust optimal process parameters were determined by robust multivariate optimization to be 1467 rpm rotational speed and 11 mm/min traverse velocity.

In the present study, a technique has been addressed in order to model and optimize gas tungsten arc welding (GTAW) process which is one of the mostly used welding processes based on the high quality fabrication acquired. The effects of GTAW process variables on the joint quality of AISI304 stainless steel thin sheets (0.5 mm) have been investigated. The required data for modeling and optimization purposes has been gathered using Taguchi design of experiments (DOE) technique. Next, based on the acquired data, the modeling procedure has been performed using regression functions for two outputs; namely, heat affected zone (HAZ) width and ultimate tensile stress (UTS). Then, analysis of variance (ANOVA) has been performed in order to select the most fitted proposed models for single-objective and multi-criteria optimization of the process in such a way that UTS is maximized and HAZ width minimized using simulated annealing (SA) algorithm. Frequency, welding speed, base current and welding current are the most influential variables affecting the UTS at 22%, 21%, 20% and 17% respectively. Similarly, base current, welding current, frequency and welding speed affect the HAZ at 28%, 20%, 16%, and 15% respectively. Based on the results considering the lowest values for current results in the smallest amount of HAZ. By the same token in order to acquire the largest amount of UTSs the highest values of current must be considered. Setting welding and base current, frequency, speed, and debi at 42 and 5 apms, 46 Hz, 0.4495 m/min, and 5 lit/min respectively resulted the optimized HAZ and UTS simultaneously. The proper performance of the proposed optimization method has been proved through comparison between computational results and experimental data with less than 6% error.

This study aims to fabricate an optimum interface surface for intracochlear catheter applications. The samples were first fabricated of two-component liquid dimethyl siloxane by designing and fabricating a mold, and then the assembly underwent surface treatment using a plasma irradiation device. The water contact angle test results showed an increase in the surface hydrophilicity of this material that water drop contact angle of origin silicone is 105° that after treatment decrease to 60°, which has the property of reducing the effect of cellular cutting in the inner ear when passing through the scala tympani. The surface engagement during passage was also minimized with an increase in surface roughness at the nanoscale. SEM and AFM photomicrographs and nano graphs show that the morphology of catheter surface in nanoscale changed and roughness increased, which is desirable for this purpose. The cell viability test results showed an improved adhesion and cell growth on the modified surface and origin silicone, and 95 % viability of cells confirmed, indicating the optimal biocompatibility of the modified silicone sample. This catheter can be used in cochlear implantation and drug delivery before surgery to enhance therapeutic efficiency